1. Field of the Invention
The present invention relates to a drive mechanism for driving a movable mirror provided in a camera (e.g., an SLR camera), and in particular to a mechanism, provided in association with the drive mechanism, for suppressing bouncing of the movable mirror.
2. Description of the Related Art
In SLR cameras, a movable mirror (quick-return mirror) is provided, which is capable of moving up and down. More specifically, capable of rotating between a viewfinder light-guiding position (mirror-down position), in which the movable mirror is positioned in a photographing optical path to reflect incident light emanated from an object (object-emanated light) toward a viewfinder optical system, and a retracted position (mirror-up position), in which the movable mirror is retracted from the photographing optical path to allow the object-emanated light to travel toward a shutter. In SLR cameras which determine whether an object is in-focus using a phase-difference AF sensor, the movable mirror is provided with a main mirror and a sub-mirror, which is supported by the main mirror. The sub-mirror, which is provided as a movable mirror, moves in association with the main mirror (which is for leading object light to the viewfinder) and part of the light emanated from an object is reflected toward the AF sensor by the sub-mirror. The sub-mirror is supported to be rotatable relative to the main mirror, and operates to project into the optical path to thereby make it possible to lead the incident light to the AF sensor when the main mirror is in the viewfinder light-guiding position (mirror-down position). When the main mirror is retracted to the retracted position, the sub-mirror also operates and moves out of the optical path.
Upon the movable mirror rotating and bouncing (vibrating) upon impact against a positioning memer, vibrations of the movable mirror can cause image shake and disturb improvement in continuous shooting speed. Accordingly, various mechanisms for suppressing such bouncing of the movable mirror have been proposed. In the related art, bounce suppression of the main mirror has chiefly been taken into consideration; however, if the demand for vibration isolating performance and continuous shooting (photographing) performance becomes high, it is required to suppress not only the bouncing of the main mirror but also the bouncing of the sub-mirror. For instance, if the sub-mirror bounces upon the main mirror rotating to the viewfinder light-guiding position, a distance measuring operation cannot be performed until the sub-mirror comes to a standstill, so that it is required to suppress bouncing of the sub-mirror when the main mirror is in a mirror-down state to improve continuous shooting speed. In addition, if the sub-mirror bounces to thereby cause mechanical shock upon the main mirror rotating to the retracted position, this shock (mirror shock) becomes a cause of camera shake (image shake), so that it is required to suppress the bouncing of the sub-mirror even when the main mirror is in a mirror-up state (retracted state). As a countermeasure for this problem, vibrations of the sub-mirror can be controlled by adjusting the operating speed of the main mirror by the setting of the cam profile of the cam mechanism for controlling rotation of the main mirror. Alternatively, a mechanism which forcibly holds down the operation of the sub-mirror by engaging a groove which is formed in a holding member for the sub-mirror with a projection-like restrictive member which is formed inside the mirror box when the main mirror rotates to the viewfinder light-guiding position has been proposed in Japanese Unexamined Patent Publication No. H09-274250.
In regard to pursuing higher levels of vibration isolating performance and continuous shooting performance, there have been limitations in effectively controlling vibrations of the sub-mirror simply by adjusting the operating speed of the main mirror by the setting of the cam profile of the cam mechanism. Additionally, in the mechanism disclosed in the above-mentioned Japanese Unexamined Patent Publication No. H09-274250, if the operation timing deviates even slightly, the restrictive member becomes incapable of being smoothly inserted into the groove of the sub-mirror holding member, thus extremely rigorous accuracy control is required.